The present invention pertains to prosthetic implants and more particularly to inner body spinal prosthetic implants to fuse two or more vertebrae together.
U.S. Provisional Application Ser. No. 60/121,705, filed Feb. 25, 1999 entitled xe2x80x9cSpinal Fusion Implantxe2x80x9d is incorporated by reference.
The human spine is made up of a column of thirty-three bones and their adjoining structures. The vertebrae near the head are known as the presaccral vertebrae which are separate bones capable of individual movement. The bodies of these vertebrae are connected by anterior and posterior ligaments and by disks of fibrocartilage generally known as intervertebral disks. These disks are positioned between opposite faces of adjacent vertebral bodies. This column of vertebrae and intervertebral disks form a central axis that supports the head and torso. These vertebrae also enclose an opening through which the spinal cord passes therebetween.
The presaccral vertebrae are normally held in position to one another by the intervertebral disks, ligaments and musculature of the body. These vertebrae move relative to adjacent vertebrae thus permitting the head to be turned relative the body and providing a wide range of flexibility to the spine.
One of the most costly health problems to society involves back pain and pathology of the spine. These problems can affect individuals of all ages and can result in great suffering to victims. Back pain can be caused by several factors such as congenital deformities, traumatic injuries, degenerative changes to the spine and the like. Such changes can cause painful excessive motion, or collapse of a motion segment resulting in the contraction of the spinal canal and compresses the neural structures causing debilitating pain, paralysis or both which in turn can result in nerve root compression or spinal stenosis.
Nerve conduction disorders can also be associated with invertible disks or the vertebrae themselves. One such condition is herniation of the intervertebral disk, in which a small amount of tissue protrudes from the sides of the disk into the foramen to compress the spinal cord. A second common condition involves the development of small bone spurs, termed osteophytes, along the posterior surface of the vertebral body, again impinging on the spinal cord.
Upon identification of these abnormalities, surgery may be required to correct the problem. For those problems associated with the formation of osteophytes or herniations of the intervertebral disk, one such surgical procedure is intervertebral diskectomy. In this procedure, the involved vertebrae are exposed and the intervertebral disk is removed, thus removing the offending tissue, or providing access for the removal of the bone osteophytes. A second procedure, termed a spinal fusion, may then be required to fix the vertebrae together to prevent movement and maintain a space originally occupied by the intervertebral disk. Although this procedure may result in some minor loss and flexibility in the spine, due to the relatively large number of vertebrae, the minor loss of mobility is typically acceptable.
During a spinal fusion following a diskectomy, a prosthetic implant or spinal implant is inserted into the intervertebral space. This prosthetic implant is often a bone graft removed from another portion of the patient""s body, termed an autograph. The use of bone taken from the patient""s body has the important advantage of avoiding rejection of the implant, but has several shortcomings. There is always a risk in opening a second surgical site in obtaining the implant, which can lead to infection or pain for the patient, and the site of the implant is weakened by the removal of bony material. The bone implant may not be perfectly shaped and placed, leading to slippage or absorption of the implant, or failure of the implant to fuse with the vertebrae.
Other options for a graft source of the implant are bone removed from cadavers, termed allograft, or from other species, termed a xenograft. In these cases while there is the benefit of not having a second surgical site as a possible source of infection or pain, there is increased difficulty of the graft rejection and the risk of transmitting communicable diseases.
An alternative approach is using a bone graft or to use a manufactured implant made of a synthetic material that is biologically compatible with the body and the vertebrae. Several compositions and geometries of such implants have been utilized, ranging from simple blocks of material to carefully shaped implants, with varying success.
There has been an extensive number of attempts in developing an acceptable prosthetic implant that can be used to replace an intervertebral disk and yet maintain the stability of the intervertebral disk spaced between adjacent vertebrae, at least until complete arthrodesis is achieved. These prosthetic implants have taken many forms. While many types of synthetic prosthetic devices have been proposed, the success ratio has been low and the surgical procedures have been complicated and often traumatic to the patient.
One of the more prevailing designs of these prosthetic implants takes form of a cylindrical implant. These types of prosthetic implants are represented by Brantigan U.S. Pat. No. 4,878,915 and Ray U.S. Pat. No. 4,961,740. In these cylindrical implants, the exterior portion of the cylinder can be threaded to facilitate insertion of the prosthetic device. Some of these prosthetic implants are designed to be pounded into the intervertebral disk space and the vertebral end plates. These types of devices are represented in Brantigan U.S. Pat. No. 4,834,757 and Brantigan U.S. Pat. No. 5,192,327. The Brantigan and Ray patents all disclose prosthetic implants wherein the transverse cross-section of the implant is constant throughout the length of the implant and is typically in the form of a right circular cylinder.
Other prosthetic implants have been developed that do not have a constant cross-section. For instance, the patent to McKinna U.S. Pat. No. 4,714,469 shows a hemispherical implant with elongated protuberances that project into the vertebral end plate. The implant of Bagby U.S. Pat. No. 4,934,848 is in the form of a sphere which is positioned between the centrums of the adjacent vertebrae.
The various prosthetic implants can be generally divided into two basic categories, namely, solid implants and implants that are designed to encourage bone ingrowth. Solid implants are represented by U.S. Pat. Nos. 4,878,915 and 4,349,921. The remaining patents discussed above include some aspect that permits bone to grow across the implant. It has been found that devices which promote natural bone ingrowth achieve a more rapid and stable arthrodesis. These implants are typically filled with autologous bone prior to insertion into the intervertebral disk space. These implants typically include apertures which communicate with openings in the implant, thereby providing a path for tissue growth between the vertebral end plate and the bone or bone substitute within the implant. In preparing the intervertebral disk space for a prosthetic implant, the end plates of the vertebrae are preferably reduced to bleeding bone to facilitate tissue growth within the implant.
A number of difficulties still remain with the many prosthetic implants currently available. While it is recognized that hollow implants which permit bone ingrowth in the bone or bone substitute within the implant is an optimum technique for achieving fusion, most of these devices have difficulty achieving this fusion, at least without the aid of some additional stabilizing device, such as a rod or plate. Moreover, some of these devices are not structurally strong enough to support the heavy loads applied at the most frequently fused vertebral levels, mainly those in the lower lumbar spine.
There has been a need for providing a prosthetic implant that optimizes the bone ingrowth capabilities and strong enough to support the vertebrae until arthrodesis occurs. There is a further need for such an implant that is capable of maintaining or restoring the normal spinal anatomy at the instrumented segment. There is also a need for an implant that exhibits reduced slippage when inserted between vertebrae and diminishes the occurrence of nerve pinching.
The present invention pertains to an improved implant and more particularly to an improved prosthetic implant used to facilitate in the fusion of two or more vertebrae.
In accordance with the principal feature of the present invention, there is provided a prosthetic implant that is formed of a biologically compatible material for use in humans. The prosthetic implant is shaped and sized for insertion between two vertebrae. In one specific embodiment, the prosthetic implant is designed to be placed in the intervertebral disk space that was formerly occupied by an intervertebral disk. The intervertebral disk is partially or completely removed prior to insertion of the prosthetic implant between the vertebrae. In one specific embodiment, the shape and size of the cage is selected to have an anatomically correct shape. In another embodiment, the prosthetic implant is shaped to increase the area of contact with the vertebrae and/or to closely emulate the region formerly occupied by the intervertebral disk. In still another embodiment, the prosthetic implant is designed to be readily inserted by established surgical procedures, with minimal chances of surgical difficulty. In yet another embodiment, the geometry of the implant ensures proper load bearing, desired load bearing and support through the fused vertebrae minimizing the likelihood of the prosthetic implant dislocating relative to the vertebrae either during surgery or during the post operative fusing process.
In accordance with another aspect of the present invention, there is provided a prosthetic implant which includes a cage having a top wall, a bottom wall, a front end wall, a back end wall, a first side wall, and a second side wall. In one embodiment, the cage is made of a material that is inert or biologically compatible with the vertebrae. The material of the cage includes, but is not limited to, bone, stainless steal, titanium, chrome, cobalt, polycarbonate, polypropelene, polyethylene, polymethylmethacrylate, polysolfone types filled with glass and/or carbon fibers, and various types of carbon and fiber reinforced polymers. In accordance with another embodiment, the cage is designed to maintain a tension load of about ten to forty pounds and more preferably about fifteen to thirty-five pounds on the disk tissue. This tension load facilitates in maintaining the cage in position between the vertebrae and accelerates bone ingrowth between the vertebrae. In still another embodiment, the cage is made of a material which closely approximates the elasticity of the vertebra. In still yet another embodiment, the cage is coated with and/or made up of material which is radiolucent to enhance the visibility of the implant when exposed to X-rays.
In accordance with still another aspect of the present invention, the first side wall and second side wall of the cage of the prosthetic implant extends substantially along the longitudinal axis of the cage and wherein the two side walls are configured to enhance the stability of the cage within the intervertebral disk space. In one embodiment, the first and/or second side wall is at least partially arcuate. In another embodiment, the first and second side wall have different face configurations. In one specific embodiment, the first side includes an arcuate surface and the second side has a substantially flat or planar surface. In one specific embodiment, the first side wall has a substantially uniform arcuate surface. In another specific embodiment, the actuate surface has a radius of curvature of about 2 to 30 degrees. In cage configurations having an arcuate first side wall surface, the cage is positioned in the intervertebral disk space such that the substantially flat or planar surface of the second side is positioned closely adjacent to the spinal cord and the first side is positioned adjacent the peripheral edge of the intervertebral disk space. Prosthetic implant cages having an arcuate or curvilinear side wall have been found to more closely conform to the surfaces with the intervertebral disk space thereby resulting in a higher degree of success for fusing together two vertebrae. The different side configurations of the cage also function as a visual aid to ensure that the cage is properly oriented between two vertebrae.
In accordance with yet another aspect of the present invention, the cage of the prosthetic implant includes a top wall and/or bottom wall having at least one rigid surface adapted to engage the underside surface of a vertebrae within the intervertebral disk space. The ridge is designed to secure or bite into the vertebrae surface. In one embodiment, the top wall includes a plurality of ridged surfaces. In another embodiment, the bottom wall includes a plurality of ridged surfaces. The ridged surfaces on the top and/or bottom wall can have a number of configurations. In one specific embodiment, the ridges have diamond shaped surfaces, thereby functioning similar to teeth-like structures. In another specific embodiment, the ridge is a uniform structure extending over the lateral and/or longitudinal surface of the top and/or bottom wall. In another embodiment, the ridges are positioned on the top end and/or bottom wall and are spaced from the outer peripheral edge of the bottom and/or top wall. In still another embodiment, the top and bottom wall have similar ridge configurations and a similar number of ridges; however, it can be appreciated that the top and bottom wall can have different numbers and/or different configurations of ridges. In still yet another embodiment, the ridges in the top and/or bottom wall of the cage anchor the cage in between the vertebrae and provide channels for bone ingrowth which facilitates in the fusion of the vertebrae.
In accordance with still yet another aspect of the present invention, the cage of the prosthetic implant includes one or more openings in one or more of the walls of the cage. In one embodiment, the openings are designed to receive materials which facilitate in the fusion of the vertebrae, facilitate in the positioning of the cage between the vertebrae, and/or secure the cage in place within the intervertebral disk space. In one specific embodiment, one or more of the openings are designed to receive a packing material which facilitates in the formation of a graft between two vertebrae. Such packing material can include, but is not limited to, medicine, human tissue, animal tissue, synthetic tissue, human cells, animal cells, synthetic cells, and the like. In another specific embodiment, the cage includes a plurality of openings to allow blood supply to grow from the sides of the cage to the vertebrae between the cage. In still another specific embodiment, one or more openings in the cage are filled with a packing material which includes one or more components that are selected to grow out of the openings of the cage radially, longitudinally and/or vertically from the cage and grow into the bone tissue of the adjoining adjacent vertebrae. In still another specific embodiment, one or more openings are filled with bone material or a synthetic material, with or without a bone activating matter such as hydroxyapatite bone or phallic protein, bone growth factor, or cartilage activation factor. In yet another embodiment, the top and/or bottom wall of the cage have an opening which communicates with an internal cavity of the cage. In still yet another embodiment, the top and bottom walls include at least one opening that are substantially the same shape and size. In accordance with another embodiment, the first side wall, second side wall, front end wall and/or back end wall include at least one opening adapted to receive an instrument for guiding and/or inserting the cage between the vertebrae of the spine by an anterior, posterior, lateral and/or latroscopic approach into the spinal column. The openings allow a surgeon to select which approach is best for inserting the prosthetic implant in the intervertebral disk space. In one specific embodiment, the instrument opening includes a securing mechanism, such as, but not limited to, a thread, in the opening to secure the instrument within the opening.
In accordance with another aspect of the present invention, at least one or more edges of the cage are rounded off so as not to be sharp. The rounding off of the edges reduces and/or eliminates pinching of the nerve leading from the spinal cord which can result in pain, damage or paralysis to the individual. The rounded edges avoid or minimize nerve pressure that can be exerted on the nerves intervertebrally exiting the spinal cord. The one or more rounded off edges also facilitates with the insertion of the cage within the intervertebral disk space. In one specific embodiment, the lateral edges of the cage are rounded off. In another specific embodiment, all the edges of the cage are rounded off.
In accordance with still another aspect of the present invention, the top wall and/or bottom wall are at least partially inclined along the longitudinal axis of the cage. In one embodiment, the top wall and/or bottom wall are uniformly inclined from the back end wall to the front end wall. In one specific embodiment, the back end wall is higher than the front end wall. In another specific embodiment, the angle of inclination of the top and/or bottom wall is about 0.5 to 15 degrees and preferably about 1 to 10 degrees and more preferably about 3 to 8 degrees. The inclination of the top and/or bottom wall of the cage facilitates in the ease of insertion into the vertebrae column and/or provides a better fit for the cage within the intervertebral disk space since the inclination better matches the anatomical shape of the space between the vertebrae of the spinal column. In accordance with another embodiment, the inclined top and/or bottom wall of the cage accommodate the positioning of the cage between two vertebrae of the spinal column and the ridges on the top and/or bottom wall of the cage are adapted to contact the surfaces of the vertebrae bone and secure the cage in position between the vertebrae until the fusion of the vertebrae is complete.
In accordance with yet another aspect of the present invention, the top wall and/or bottom wall are at least partially inclined between the first and second side wall of the cage. In one embodiment, the top wall and/or bottom wall are uniformly inclined from the first and second side wall. In one specific embodiment, the second side wall is higher than the first side wall. In another specific embodiment, the angle of inclination of the top and/or bottom wall is about 0.5 to 15 degrees and preferably about 1 to 10 degrees and more preferably about 3 to 8 degrees. The inclination of the top and/or bottom wall of the cage facilitates in the ease of insertion into the vertebrae column and/or provides a better fit for the cage within the intervertebral disk space since the inclination better matches the anatomical shape of the space between the vertebrae of the spinal column.
In accordance with another aspect of the present invention, a pair of cages are used to support and/or fuse two vertebrae in the spinal column. In one embodiment, the cages are positioned in a side by side relation to form a rigid transverse strut between adjacent vertebrae.
It is an object of the present invention to provide an improved prosthetic implant for insertion between two vertebrae.
It is another object of the present invention is to provide a prosthetic implant which better emulates the space between the vertebrae.
Yet another object of the present invention to provide a prosthetic implant which includes one or more ridges to help secure the prosthetic implant in position between the vertebrae.
It is yet another object of the present invention to provide a prosthetic implant which is used in a side by side relation to form a rigid transverse strut between adjacent vertebrae.
It is still yet another object of the present invention to provide a prosthetic implant which provides improved spinal support fixation and methodology which provides stability between adjacent vertebrae and the shape will facilitate in securing the prosthetic implant between the vertebrae.
Another object of the present invention is to provide an apparatus which will aid in the positioning of the prosthetic implant between the vertebrae.
Still yet another object of the present invention is to provide a prosthetic implant which has one or more openings that can receive packing material to facilitate in the fusion of two adjacently positioned vertebrae.
A further object of the present invention is to provide a prosthetic implant which can be easily and efficiently positioned between two vertebrae and which reduces the failure rate of prosthetic implants between the vertebrae.
It is another object of the present invention to provide a prosthetic implant which includes one or more sloped surfaces to facilitate in the insertion of the prosthetic implant between the adjacently positioned vertebrae and to better match the shape of the prosthetic implant to the space between the adjacently positioned vertebrae.
It is still another object of the present invention to provide a prosthetic implant which includes surfaces that reduce pinching with the spinal cord and other body parts closely adjacent to the prosthetic implant.
It is another object of the present invention to provide a prosthetic implant that is made of a biologically compatible material.
It is another object of the present invention to provide a prosthetic implant that is made of and/or coated with a radiolucent material.
It is another object of the present invention to provide a prosthetic implant that is made of a material which closely approximates the elasticity of the vertebra.
These and other objects of the invention will become apparent to those skilled in the art upon reading and understanding the following detailed description of preferred embodiments taken together with the drawings.